Rear extension + dormer loft conversion, Ruislip

Brief

A 1936 detached mock-Tudor in Eastcote, Ruislip — HA4, not in a conservation area, PD rights intact. The clients (couple with two teenage children) had been in the property for 15 years and were planning to remain long-term. The property at 138m² had three bedrooms and one bathroom — adequate but tired, with a poorly laid out 1980s kitchen-diner extension at the rear (a 14m² lean-to with cold concrete floor and inadequate insulation). The brief: replace the failing 1980s extension with a high-spec single-storey rear extension; convert the loft to add a master suite; refurbish the existing layout. Total budget: £215,000.

Challenge

Four site challenges. (1) Removing the existing 1980s lean-to extension: the extension had been built with reused 9-inch solid brick walls (rather than cavity construction) sitting on shallow strip footings (700mm depth) over made-ground fill. Demolition needed careful temporary support of the original house rear wall (which had been load-bearing on the extension wall through a wall-tie connection added in 1986). Structural engineer specified a goalpost steel frame to temporarily carry the original rear wall load during demolition and rebuilding. (2) New rear extension PD compliance: the existing 1980s extension footprint counted as 'previously extended' for permitted development calculations — any new extension had to fit within remaining PD allowance (4m projection from original rear wall for a detached). The new 5m × 6m extension proposed exceeded PD; Larger Home Extension Prior Approval submitted (6m × 8m × 4m height); approved at 8 weeks following one neighbour objection (resolved through revised guttering detail). (3) Loft conversion: existing loft head height was 2.3m at ridge — below the 2.4m minimum for Class B PD loft conversion habitable use. Solution: full planning application (not PD) to add a rear dormer with rear roof structure modifications to achieve compliant head height; approved at 10 weeks. (4) Whole-house programme: 22-week site programme with family remaining in property for first 8 weeks (loft works only) then vacating for 14 weeks (rear extension + ground floor refurb). Temporary accommodation cost factored into client budget.

Solution

Pre-planning: full planning for rear dormer loft (10 weeks approval); Larger Home Extension Prior Approval for rear extension (8 weeks approval with revised guttering detail). Phase 1 (weeks 1–8, family in residence): rear dormer loft conversion. Existing loft stripped; new structural floor with 175mm joists between existing rafters; rear roof partially demolished and rebuilt with new flat-roof dormer (8m wide × 4m deep dormer); new staircase from first-floor landing replacing existing access hatch; master bedroom 18m² + walk-in wardrobe 4m² + en-suite 5m². Velux GGL UK10 (1340×1600mm) to front pitched slope; flat rooflight 1.5m × 1m to dormer flat roof; ventilated via concealed extract through party wall. Loft works completed at week 8 with family relocating to short-stay rental for the remainder. Phase 2 (weeks 9–22, family vacated): full demolition of 1980s rear lean-to using temporary goalpost steel support of original house rear wall; new strip foundations (450mm wide × 1.0m depth) on London Clay; new 5m × 6m single-storey rear extension; vaulted ceiling with 6m × 1.5m roof lantern (Glazing Vision Lumin) for daylight modelling; 4.8m Reynaers CF 77 bifold to garden; integrated boot room and pantry off side return between extension and existing kitchen. Ground floor whole-house refurb: removed internal walls between original kitchen, dining room and existing rear lean-to footprint to form 38m² open-plan kitchen-diner; new Magnet Linea handleless kitchen with quartz worktop and Bora downdraft induction hob; Crittall-style internal screen (AluK F82, matt black, 3m × 2.5m, with single hinged door) dividing kitchen-diner from new ground-floor study/snug. Heating: existing 1995 boiler decommissioned; new Vaillant Ecotec Plus 38kW combi boiler installed in repurposed under-stairs cupboard; 14 new radiators sized for upgraded fabric. EPC: D (62) → B (84) — combined dormer roof insulation + rear extension fabric + loft insulation + new boiler + LED throughout.

Outcome

Floor area added: 52m² (30m² rear extension net of demolished 14m² lean-to = 16m² net + 27m² dormer loft conversion = 43m² net new habitable floor area; total floor area 138m² → 181m²). Property uplifted from 3-bed/1-bath to 4-bed/2-bath/study/walk-in-wardrobe master suite. EPC: D (62) → B (84) — exceeds typical renovation EPC targets. Build delivered at 22 weeks within programme; final spend £218,500 against £215,000 budget (1.6% over due to revised guttering detail from planning condition). Property valuation: pre-renovation £680,000; post-renovation £965,000 (£285,000 gross value uplift on £218,500 build cost — 30% ROI). Family relationship with property significantly improved: 'the house we always wanted'. Builderr maintained 5-year warranty on structural works; 2-year warranty on M&E; 1-year warranty on decoration.